Why has National remained so incredibly popular for so long despite suffering continuing calamities, embarrassments and unwanted distractions, many of them self-inflicted?

Labour MPs this week went on the front foot, castigating National as a Government "mired in scandals and more interested in deals with its mates" than governing in the country's best interests. David Cunliffe, one of those MPs, went as far as describing John Key's second-term Administration as "the rotting carcass on the body politic".

Cunliffe provided a long, but not exhaustive list of National's follies, including in no particular order: Warner Bros' muscle-flexing on The Hobbit, the Government's generosity in helping out radio and TV company MediaWorks, "Banksie" and Kim Dotcom, the failings of the Government Communications Security Bureau, the plunge into debt of state coal company Solid Energy, the dreadfully slow introduction of ultrafast broadband, backdowns on taxing employer-provided carparks and cellphones and unemployment running at close to 7 per cent.

The public was counting the score, Cunliffe added. In short, National was on its way out.

Well not quite. This week's Herald-DigiPoll survey put matters into perspective. Backing for Labour rose by more than four percentage points on the previous poll last August, the party registering more than 36 per cent of the committed vote. It is Labour's best showing since late 2010.

But National edged up by a percentage point to 48.5 per cent, thus maintaining a dominance in the poll dating back to John Key taking hold of National's reins in late 2006.

Cunliffe's catalogue of calamities plus the inevitable wear and tear on a second-term Government would have been expected to have a detrimental effect on National's fortunes.

Instead, Key-led National continues to enjoy a golden run in the poll which now stretches back some 300-plus weeks.

The questions are obvious. How have Key and National managed to defy political gravity and, perhaps more pertinently, for how much longer will they be able to do so?

It is possible to list at least 10 factors as being responsible, some of them clear-cut and others simply untested gut-feeling hypothesising.

The first factor is Key's sky-high rating as most preferred Prime Minister. This is crucial in drawing many tens of thousands of uncommitted voters plus those with weak attachments to other parties to tick National. The "brain fades" and other lapses of last year, a horror year for him and National, seem to have had little, if any, effect on Key's personal rating.

Labour has long targeted "Brand Key" in the belief that destroying him will destroy National. The strategy may have backfired, revealing Labour as petty and small-minded. Key's failings may instead be viewed by the electorate as human, thereby increasing his rapport with voters.

Second, Key's moderate conservatism is very much in tune with the prevailing mood of the wider New Zealand electorate. Helen Clark understood that reality. But she still eventually fell victim to the conservative public's near hatred of Labour's supposed political correctness.

Third, Key is unashamedly pragmatic - a word that used to be anathema to purists who stood four-square behind Sir Roger Douglas and Ruth Richardson in the 1980s and early 1990s. No longer. Ideology takes a back seat with Key. There is no lecturing of the public as to the kind of policy prescription that ought to be swallowed. There is instead a "no surprises" approach, by and large. And the Government does what it says it will do.

Even National's showcase policy of partial privatisation has a pragmatic element in the retention of a majority government shareholding.

The fourth factor is the neutralising of troublesome issues rather than allowing them to linger and fester.

In terms of resources, Steven Joyce has thrown the political equivalent of the kitchen sink at the faults in the Novopay payroll system for teachers. No doubt he would chuck the real thing in Talent2's direction if it might help.

Fifth comes the economy ... Labour's recent private polling has confirmed a majority of voters view National as the better manager of the economy. They are likely to continue to do so in uncertain economic times. Why? Because Key and Bill English have a proven track record in handling crises, like the Christchurch earthquakes, in a calm and unflustered fashion.

The Herald-DigiPoll survey had a majority of 49 per cent to 43 per cent agreeing the Government is moving in the right direction. National's Achilles heel can be summed up in three words - jobs, jobs and jobs. However, there are signs the economy is slowly picking up steam - as evidenced by this week's gross domestic product figures for the last quarter of last year.

Sixth, National may have issued various vision documents which have ended up propping up shelves around Beehive. But the party is not all that good at articulating those visions. It is good, however, at maintaining momentum. It is essential that a Government be seen to be busy, Otherwise, it looks like it has stalled. - and that is fatal.

Seventh, National is still largely defining what the arguments are about in most policy areas. By doing so, it's halfway to winning those arguments. Labour has yet to thrust a new dynamic - for example, a more hands-on style of economic management - on to the political agenda and lead debate on its terms.

Eighth, opposition parties are instead still devoting considerable time and effort to fighting battles they have lost - such as partial privatisations. Or trying to land hits on National by raking over the coals of history - Solid Energy being the prime example.

Ninth, the public may be getting acclimatised to the at times rather chaotic nature of minority government.

Clark's third term was marred by constant sideshows and distractions. Key's second term has been similarly afflicted. But it has not been damaged. Voters may now be more willing to accept (or simply ignore) the ever noisier political static if they can be assured National is focused on the bigger picture and getting things done.

Tenth and last, the political temperature is benign in terms of governing. Apart from asset sales there are few, if any, issues that are seriously divisive and on which National finds itself stranded on the wrong side of the argument for ideological reasons. Voters may be more tolerant, if not forgiving, of politicians' occasional lapses. Hekia Parata had to get an awful lot wrong before she lost the public's confidence.

Crucially, there's no mood for change, the real government-killer, or even much hint of such a mood developing. National may still lose next year's election, but only because of an absence of coalition partners. Its real enemy is MMP mathematics. It can't do much about that.

Herald political correspondent John Armstrong has been covering politics at a national level for nearly 30 years.
Based in the Press Gallery at Parliament in Wellington, John has worked for the Herald since 1987.
John was named Best Columnist at the 2013 Canon Media Awards and was a previous winner of Qantas media awards as best political columnist.
Prior to joining the Herald, John worked at Parliament for the New Zealand Press Association. A graduate of Canterbury University's journalism school, John began his career in journalism in 1981 on the Christchurch Star. John has a Masters of Arts degree in political science from Canterbury.